Marine picocyanobacterium Prochlorococcus contributes to a vital proportion of the global primary production, especially in the nutrient-limited oligotrophic oceans. Cyanophages that infect Prochlorococcus redirect the intracellular metabolism of their cyanobacterial host, releasing a variety of dissolved organic matter (DOM) from the lysed cells, eventually affecting the global biogeochemical cycling. This thesis presents studies on the host-phage interactions of the marine cyanobacterium Prochlorococcus, combining approaches from omics-techniques, as well as physiological and biochemical assays. Analysis of the within-host proteomes during phage infection is essential for revealing the molecular dynamics of host-phage interactions. As a consequence, we have conducted quantitati...[ Read more ]

Marine picocyanobacterium Prochlorococcus contributes to a vital proportion of the global primary production, especially in the nutrient-limited oligotrophic oceans. Cyanophages that infect Prochlorococcus redirect the intracellular metabolism of their cyanobacterial host, releasing a variety of dissolved organic matter (DOM) from the lysed cells, eventually affecting the global biogeochemical cycling. This thesis presents studies on the host-phage interactions of the marine cyanobacterium Prochlorococcus, combining approaches from omics-techniques, as well as physiological and biochemical assays. Analysis of the within-host proteomes during phage infection is essential for revealing the molecular dynamics of host-phage interactions. As a consequence, we have conducted quantitative proteomics in two sets of relatively well-defined host-phage systems—the cyanopodovirus P-SSP7 and cyanomyovirus P-HM2 both infecting their host Prochlorococcus MED4. This work has been first time characterising the quantitative proteomics during infection of Prochlorococcus by marine cyanophages, which provides further insight into the infection dynamics and mechanism on both translational and post-translational level. Meanwhile, the lysis-induced phytoplankton-released DOM is important for the marine food web because it supports the growth of heterotrophic microorganisms. However, the impact of viral DOM on the uninfected phytoplankton remains largely unknown. We therefore examined the cyanobacterial responses towards viral lysis products. First, we have determined the elemental concentrations and amino acid compositions of the phytoplankton-derived DOM. Employing transcriptomic sequencing and biochemical assays, DOM-responsive genes and metabolism of the host Prochlorococcus have been identified and further validated. Collectively, the combined work presented herein has advanced the understandings of host-phage interactions of marine cyanobacterium Prochlorococcus, linking the infection dynamics with molecular basis on various levels.